Electric Fense RFI

Discussion in 'General Technical Questions and Answers' started by KD0QG, Jul 1, 2021.

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  1. KD0QG

    KD0QG XML Subscriber QRZ Page

    I am getting pulse fence RFI about a burst per second. I can take it out the rfi with NB on HF bands and it seems worse on some frequencies. My problem is the fence's signal over powers some of the repeater signals on VHF and UHF unless they are very strong signals. It gives a chopping sensation on the receive repeater signal. The fence is necessary to keep the cows in out here but is there some type of external noise blanker or a way to minimize the fence signal?
     
    Last edited: Jul 1, 2021
  2. WJ4U

    WJ4U Subscriber QRZ Page

    Sounds like you need some de-fense! :cool:
     
    K0UO and PU2OZT like this.
  3. W9RLG

    W9RLG Ham Member QRZ Page

    Shouldn't that read de-fence!!!!

    w9rlg
    Bob
     
  4. N9DG

    N9DG Ham Member QRZ Page

    Hopefully you are on good terms with the neighbor with the fence. The correct solution is fix the fence. Noise from electric fences is usually an indicator a poor connection somewhere in the interconnections of the fence elements, or things like gate hooks or similar. If it is that loud RF wise, then in all likelihood the main point of arching is probably audible by just walking along the fence. The actual fault may be some distance away as the RFI from a poor connection arc propagates down the wire far.

    When I was young we had miles of electric fence on the farm, I built much of it. Some sections of the electric fence were within a few 10's feet of some of my antennas. Pretty much never heard it, but if I did, then I knew that there was a problem somewhere so went looking for it, and then fixed it.

    Edit to add: Also the things that generate RFI in a fence like that also often keep it from working as well as it should be. So for the fence owner it is in their best interest to fix the problem that is generating the RFI.
     
    Last edited: Jul 1, 2021
    KD0QG, WS4JM, WA8FOZ and 4 others like this.
  5. PU2OZT

    PU2OZT Ham Member QRZ Page

    For myself, I probably will never be able to get noises from adjacent fences fixed from part of those stupid (read = «new-rich brazilians») high rise condos around me. Add their s**t garage door automatism, and stupid non-working chinakrap leds or whatever.
    Already made up my mind.
    Good luck, however, for you, still able to change things a tad.

    Oliver
     
  6. N0TZU

    N0TZU Platinum Subscriber Platinum Subscriber QRZ Page

    If you are having that much interference on VHF FM it must be really bad, or extremely close!

    We had electric fences for horses here and they didn’t make much noise because I made them correctly and maintained them. Our elderly neighbors were a different story, because they never connected wires together very well and there were myriad places that had tiny arcs with each pulse. We were good friends with them so I offered to find the worst connections and fix them, which they gladly accepted.

    I used a portable radio and walked the fences to find the worst splices and corrected them. Much better. The rest was taken care of quite well by the noise blanker (on HF).

    Another possibility is vegetation that has grown up to touch the wire, or that the connection from the fencer to the ground rod is bad.

    If the fences use tape or rope rather than wire, there can be breaks in the tiny wire strands woven in. There’s no practical way to splice these so you have to use a connector plate over the break. Also it doesn’t work to tie the tape/rope together because not all the strands get connected.
     
    Last edited: Jul 1, 2021
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  7. SM0GLD

    SM0GLD Ham Member QRZ Page

    When the grass grows high it may come in contact with the fence wire and that will cause arcing.
    The grass under the fence wire must be cut all the time.
     
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  8. NK7Z

    NK7Z XML Subscriber QRZ Page

    You might have the fence owner checks the ground at the fence power point(s). A bad ground can cause this sort of RFI. Of course, remind them to follow all safety procedures, and to not work on the fence unless they know what they are doing.
     
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  9. N0TZU

    N0TZU Platinum Subscriber Platinum Subscriber QRZ Page

    Another possibility is insulated wire run underneath gates or fastened to buildings. Some people try to use common insulated house wire for this which will breakdown at the voltage involved and arc to objects. Use the heavily insulated wire made for the purpose and sold at farm and ranch stores along with all the other electric fence items.

    Also very dirty, cracked, or missing insulators can be a problem.
     
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  10. N9DG

    N9DG Ham Member QRZ Page

    Generally my experience was that arcs to ground weren't nearly as big a problem for RFI as arcs between segments of fence where the remaining stretch of fence became an antenna that was well insulated from the ground.

    Yes plants growing into the fence needed routine attention, the fence controller unit was a "weed burner", which it did indeed do. But only for one or two smallish plants at a time. So large amounts of plant growth needed to be dealt with other ways. A long blade machete worked well for the kind of maintenance. This was back in the days before string trimmers becoming so ubiquitous.
     
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